Perimenopause is the period of time before actual menopause occurs and is often characterized by irregular menstrual cycles due to fluctuating estrogen levels. Hot flushes (warmth that begins on the face and radiates to the neck and chest, often accompanied by red flush) are experienced by approximately 80% of women once circulatory estrogen levels are decreased. Certain plant chemicals called phytoestrogens can modify or mimic the action of reproductive hormones in humans and whose biological actions suggest that they may provide natural protection for women from symptoms such as hot flushes. This study will test two doses of isoflavones, a phytoestrogen in a soy dietary supplement for the treatment of hot flushes in perimenopausal and menopausal women.